Twin fin fairing

ABSTRACT

A fairing for the reduction of vortex-induced vibration and the minimization of drag about a substantially cylindrical element immersed in a fluid medium. The fairing also eliminates the galloping phenomenon typically associated with a teardrop-shaped fairing. The fairing having a U-shaped cylindrical shell with opposing edges defining a longitudinal gap and parallel fins extending outwardly from the opposing edges of the shell, the parallel fins being positioned so as to reduce vortex-induced vibration, minimize drag and to eliminate the galloping phenomenon on the cylindrical element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 11/463,413filed Aug. 9, 2006, now U.S. Pat. No. 7,337,742 issued Mar. 4, 2008which is herein incorporated in its entirety.

TECHNICAL FIELD

The present invention relates generally to the reduction ofvortex-induced vibration (“VIV”) and more particularly to a fairing usedfor the reduction of VIV on pipes or other structural componentsimmersed in a fluid.

BACKGROUND OF THE INVENTION

Exploration for oil and natural gas reserves led drillers offshore manyyears ago and as offshore exploration continues, offshore producers findthemselves in deeper and deeper waters. While those waters may bring thereserves they seek, the offshore producers are also faced with strongercurrents threatening the structural integrity of their risers,pipelines, and other elongated and cylindrical components involved inoil and gas production.

Stresses on the pipes or other structural components immersed in fluid,such as drilling risers, production risers, pipelines, structuraltendons, etc. greatly increase as the velocity of the current increasesand the stresses are magnified as the depth of the water and length ofthe risers at the well location increases. When operating rigs in highcurrent areas, the riser is exposed to currents that can cause at leasttwo kinds of stresses. The first is caused by vibration resulting fromvortices shed off a component when fluid flows by. That vibration,occurring perpendicular to the current, is referred to as“vortex-induced vibration,” or “VIV.” When water flows past the riser,it may cause vortices to be alternatively shed from each side of theriser when Reynolds Numbers reach a certain range. If the frequency ofthis harmonic load is near the resonant frequency of the riser, largevibrations transverse to the current can occur. The second type ofstress is caused by the drag forces that push the riser in the directionof the current due to the riser's resistance to fluid flow. The dragforces are significantly amplified by the vortex-induced vibrations ofthe riser, i.e. a vibrating pipe. A riser pipe that is vibrating due tovortex shedding will disrupt the flow of water around it more than astationary riser or a non-vibrating pipe. This results in more energytransfer from the current to the riser, and hence more drag.

The movement of oil and gas exploration, development and production intodeep and ultra-deep waters has created unique engineering challengesrequiring innovative engineering solutions. One particular challenge isthe vortex-induced-vibrations (VIV) of long drilling and productionrisers. As discussed above, when long elements such as subsea pipelines,risers, tendons, umbilicals and cables are affected by relatively strongcurrents over extended lengths along the element, the currents may causevortices to be shed from the sides of the element in an alternatingmanner which can induce VIV. The resulting vibration increases drag,reduces fatigue life and left unchecked may lead to the failure of themarine element or its supports.

Shrouds, strakes and fairings have traditionally been added to risersand other submerged pipes in order to minimize the current-inducedstresses on these pipes. Strakes and shrouds can be effective regardlessof the current orientation, but they tend to increase the drag acting onthe riser. By contrast, fairings are generally more efficient inreducing drag and VIV. Fairings generally comprise streamlined shapedbodies (such as airplane wings) that weathervane or rotate about theriser maintaining positions substantially aligned with the watercurrent. Fairings generally reduce vortex-induced forces and minimizedrag on the riser by reducing or breaking up the low pressure areas thatexist down-current of the riser.

One example of a fairing is found in U.S. Pat. No. 4,474,129 thatdiscloses a fairing removably mountable on risers equipped with buoyancymodules that has a tail tapering aft and a fin positioned after thetail. This fairing completely surrounds the riser and is fastenedtogether at the back portion of the fairing. Another example of afairing is found in U.S. Pat. No. 4,398,487 which describes astreamlined symmetrical structure having a nose portion, a tail portionand two opposed side portions. This fairing is formed as two shellhalves that completely surround the riser and are connected at the frontend of the nose by quick release fasteners and at the end of the tailportion by hinges. U.S. Pat. No. 5,410,979 describes a small fixedteardrop-shaped fairing that surrounds a riser and is fixed to the riserso as to not rotate. U.S. Pat. No. 6,048,136 describes a fairing that isinstalled on a drilling riser in combination with a synthetic foambuoyancy module. This fairing is formed as two shell halves thatsurround the riser and attach at the front and back portions of thefairing. A rotating fairing is described in U.S. Pat. No. 6,067,922 asincluding a copper element mounted in the annular region of the fakingto discourage marine growth. This fairing is formed as a single piecethat completely surrounds the riser and is attached at the tail orflange portion with bolts. An ultrashort fairing described in U.S. Pat.No. 6,223,672 is shown in FIG. 2. This fairing 2 has a pair of shapedsides 4A, 4B departing from the circular profile of a marine riser andconverging at a trailing edge 6. It should be noted that all of theabove described fairings are constructed in predetermined lengths and aplurality of fairings are positioned along the length of any particularriser.

While fairings can be effective for reducing VIV, a number of problemsstill exist with the prior art fairings. As illustrated in the priorart, fairings have become more and more complex in design, they oftenrequire a large number of parts, and as such, they have become morecostly to produce and maintain. Generally, fairings must be secured tothe elongated component by bands, bolts or other fasteners that mayfail. Further, the use of such fasteners adds to the cost and laborassociated with the fairing's use. Additionally, corrosion and marinegrowth frequently causes the rotational elements of a fairing to seizeup so that it can no longer rotate and properly align with the current.Such a concern has often resulted in fairings being used only on risersor other components that remain on the risers only a short period oftime, leaving those in the industry to rely upon less effective VIVreduction means such as fixed-fin vortex strakes for more permanentlyfixed components.

Although strakes with certain fin heights and fin periods can reduce theamplitude of the VIV induced motion by more than 90% and have beenproven to be effective tools, a lower drag solution would be desirable.While conventional teardrop fairings are effective in reducing both dragand VIV, users report that these devices are subject to a “galloping”motion. The causes of this galloping motion remain unclear. Therefore,there remains a need for an improved VIV suppression device that reducesvibration, that does not increase drag and is resistant to gallopingmotions.

Fairings are typically applied to drilling and/or production risers inone of two ways. In one manner of installation, fairings are placed onthe riser after it is in place, suspended between the platform and theocean floor, in which divers or submersible vehicles (referred to asROVs) are used to fasten the multiple fairings around the riser. Asecond method of installation is carried out as the riser is beingassembled on a vessel and installed. In this method the fairings arefastened to the pipe as lengths of pipes are fitted together to form theriser. This method of installation is typically performed on a speciallydesigned vessel, called an S-Lay, J-Lay barge or Reel Lay barge. AnS-Lay barge is one that has a declining ramp, positioned along a side orrear of the vessel and descending below the ocean's surface, that isequipped with rollers (referred to as a “stinger”). As the lengths ofpipe are fitted together, fairings are attached to the connected pipesections before the pipe is rolled down the ramp and into the ocean. Oneof the problems of installing fairings in this manner is that when thefins of the fairing rotate over the rollers on the ramp, the finsfrequently become damaged by the rollers. In this method ofinstallation, the completed riser laid on the ocean floor, then ispulled up to a vertical position when it reaches the appropriate lengthand is attached to the surface platform and the well head on the oceanfloor.

It would be advantageous to provide a relatively lightweight, resilientfairing that can be easily placed on a riser rather than having to befastened around the entire circumference.

It would be advantageous to provide a fairing that reduces vibration,that does not increase drag and is resistant to galloping motions.

BRIEF SUMMARY OF THE INVENTION

The subject invention is directed to a fairing for the reduction ofvortex-induced vibration, the minimization of drag and the eliminationof galloping about a substantially cylindrical element immersed in afluid medium. The fairing has a U-shaped cylindrical shell with opposingedges defining a longitudinal gap and parallel fins extending outwardlyfrom the opposing edges of the shell, the parallel fins being positionedso as to reduce vortex-induced vibration, minimize drag and to eliminatethe phenomenon of galloping on the cylindrical element. The fairing hasa length to diameter ratio of 1.5 to 2.50 and preferably a ratio of 1.75to 2.0 where the length is measured from the leading nose of the fairingbody to the end of the fins, and the diameter is the diameter of thecenter of the circle defining the shell.

The shell has an outer diameter D and the parallel fins have a distanceW between opposing edges of the fins. The ratio of W to D is from W=D toW=75% of D. The fins of the fairing can taper inward.

The fairing further includes a bearing pad configured to fit in the gapin the shell between the shell's opposing edges and the parallel fins.The bearing pad has a curved inside surface and side surfaces inparallel alignment with each of the fins. Each fairing includes aplurality of bearing pads for securing the fairing to a cylindricalelement.

The fairing further includes at least a set of opposed connectors forsecuring the fairing to a cylindrical element, each connector beingpositioned on an inside surface of each parallel fin. The fins caninclude three sets of opposed connectors. Each connector includes anopening configured to receive a fastening means for securing theopposing connectors together.

The fairing further includes a flange at a top and bottom edge of thefairing, the flange extending around the circumference of the shell andoutwardly from the shell. The flange can include one or more V-shapedcutouts for the creation of opening hinges.

Each fin on the fairing does not extend beyond the outer diameter of theshell.

The fairing is constructed from a non-metallic, low corrosive materialselected from a group consisting of polyethylene, polyurethane, vinylester resin, poly vinyl chloride and fiberglass.

The invention also includes a fairing system for the reduction ofvortex-induced vibration and the minimization of drag about asubstantially cylindrical element immersed in a fluid medium. Thefairing system has a plurality of fairings having U-shaped cylindricalshells, each shell having opposing edges defining a longitudinal gap.Parallel fins extending outwardly from the opposing edges of each of theplurality of shells, the parallel fins being positioned so as to reducevortex-induced vibration, minimize drag and the elimination of gallopingon the cylindrical element. The fairing includes means for securing eachof the plurality of fairings around the cylindrical element.

The collar includes a plurality of compliant annulus spacers extendingoutwardly from an inside surface of the collar, the spacers beingconfigured to induce frictional interaction between the collar and thecylindrical element.

The means for securing the fairings around the cylindrical elementincludes a bearing pad configured to fit in the gap in each shellbetween the shell's opposing edges and the parallel fins. The bearingpad has a curved inside surface and side surfaces in parallel alignmentwith each of the fins. Each fairing includes a plurality of bearing padsfor securing the fairing to a cylindrical element.

An alternate means for securing the fairings around the cylindricalelement include at least a set of opposed connectors, each connectorbeing positioned on an inside surface of each parallel fin. The fins caninclude a plurality of opposed connectors. Each connector includes anopening configured to receive a fastening means for securing theopposing connectors together.

The fairing further may include a flange at a top and bottom edge of thefairing, the flange extending around the circumference of the shell andoutwardly from the shell. The flange can include at least one V-shapedcutouts. The flanges on each fairing are configured such that they alloweach fairing to freely rotate on an adjoining fairing.

A circular collar can be positioned between a group of or each of theplurality of fairings and the collar being configured such that itallows each fairing to freely rotate on the collar. The collar is in twosections held together by means for securing the collar around thecylindrical element. The collar is fixed to the riser and does notrotate.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIG. 1 is a side elevational view of a drilling vessel illustrating theuse of the inventive fairings in one of the environments in which theinvention is used;

FIG. 2 is a side elevational view of a prior art fairing;

FIG. 3 is a perspective view of one embodiment of the fairing of thepresent invention;

FIG. 4 is a cross-sectional view of the inventive fairing taken alonglines 4-4 of FIG. 3;

FIGS. 5A and B is a perspective view of the fairing of FIG. 3 withbearing pads installed; is a cross-sectional view of the fairing takenalong lines 6-6 of FIG. 5;

FIGS. 6A and B illustrate a fastener for securing the bearing pads tothe fairing in FIG. 5A;

FIG. 7 is a perspective view of a bearing pad of FIG. 5;

FIG. 8 is a top plan view of the bearing pad of FIG. 7;

FIG. 9 is a perspective view of an alternate embodiment of the fairingof the present invention;

FIG. 10 is a side plan view of the fairing of FIG. 9;

FIG. 11 is a front plan view of the fairing of FIG. 9;

FIG. 12 is a cross-sectional view of the fairing taken along lines 12-12of FIG. 11;

FIG. 13 is a top plan view of the fairing of FIG. 9;

FIG. 14 is a cross-sectional view of the fairing of FIG. 9;

FIGS. 15A and B is a side plan view of a fastener for securing thefairing of FIG. 9 to a raiser;

FIG. 16 is a perspective view of a series of fairing segments of FIG. 9;

FIG. 17 is an alternate embodiment of a series of fairing segments ofFIG. 9;

FIG. 18 is a perspective view of one the collars separating the fairingsegments of FIG. 17;

FIG. 19 is a bottom plane view of the collar of FIG. 18;

FIG. 20 is a top plan view of an annulus spacer that is inserted in theinside surface of the collar of FIG. 18;

FIG. 21 is a graph of drag coefficient (Cd) for a bare pipe and theinventive fairing by Reynolds number (Re);

FIG. 22 is a graph of A* by nominal reduced velocity (Vm) for a bar pipeand the inventive fairing;

FIG. 23 is a cross-sectional view of an alternate embodiment of thefairing of FIG. 9;

FIG. 24 is top plan view of the fairing of FIG. 23; and

FIG. 25 is a graph of drag coefficient (Cd) compared to velocity (V) inwhich each line on the graph represents a different W:D ratio.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to rotating fairings that includespecifically placed fins for the reduction of vortex-induced vibration(“VIV”) on pipes or other structural components immersed in fluid. Asdiscussed above, when a solid object is exposed to fluid flows vibrationresults from vortices shed off the object when the fluid flows by it.The flow pattern around a cylinder can be characterized by the ReynoldsNumber (Re) of the incident flow and the location where flow separatesfrom the cylinder surface which depends on whether the boundary layer isturbulent or laminar. In the subcritical range, the Reynolds numberrange is 300<Re<1.5×10^5, the laminar boundary layers separate at about80 degrees aft of the leading edge of the cylinder and vortex sheddingis strong and periodic. The range 1.5×10^5<Re<3.5*10^6 is called thetransition region. In these regions the boundary layer becomes turbulentand the separation points move aft to 140 degrees and the cylinder dragcoefficient drops abruptly.

A fairing is described in U.S. Pat. No. 6,401,646 that includes acylindrical shell having opposing edges defining a longitudinal gap anda pair of corresponding fins extending outwardly in a verticaldirection. The fins are placed generally at a 120° angle relative to thecircumference of the shell. U.S. Pat. No. 6,401,646 is incorporatedherein in its entirety. During hydrodynamic testing, it has beendiscovered that a U-shaped fairing having parallel twin fins causes asubstantial reduction in VIV and drag forces and the inventive faring isnot affected by a galloping motion.

The present invention is directed to a rotatable U-shaped fairing systemhaving parallel twin fins for the reduction of VIV on pipes or otherstructural components immersed in fluid. In one embodiment, theinventive fairing is installed on drilling and production risers used inoffshore oil and natural gas exploration. FIG. 1 illustrates oneenvironment in which the inventive fairing is used. A drilling vessel orplatform 10 provides surface facilities 12. Riser 14 descends frombeneath the deck of the surface facilities 12 and is fitted with largeOD buoyancy modules which are fitted with twin fin fairings 16 below theocean surface 18. A plurality of fairings 16 are installed along theriser 14 to reduce VIV and minimize drag on the long unsupported riser14. This illustrative embodiment shows the fairing system installed on adrilling or production riser. However, cylindrical pipes are employed ina variety of other applications such as subsea pipelines; drilling,import and export risers; tendons for tension leg platforms; legs fortraditional fixed and for compliant platforms; other mooring elementsfor deepwater platforms; and so forth. Those having ordinary skill inthe art can readily apply these teachings to such other applications.

Fairing 16 is formed from a U-shaped shell 20 having opposing edges 24,26 that define a longitudinal gap G and a pair of corresponding fins 22extending outwardly from edges 24, 26 in a vertical direction (FIGS. 3and 4). The spaced apart fins 22 are parallel to each other and extendoutwardly in a direction parallel with the fluid current in order tomove the boundary layer vortex eddies further away from the riser 14without adding significant drag (FIG. 4). The fins 22 can be any length,however, regardless of the length, the fins 22 do not extend beyond thenominal outer diameter of the shell 20. Preferably, fairing 16 hasdimensions of length L to diameter D (shell diameter) such that thelength L to diameter D ratio (aspect ratio) is in the range of 1.5 to2.50, preferably in the range of 1.75 to 2.0. The shell's U-shapeprovides for a longitudinal gap G in shell 20 that allows for placementof the shell 20 around a cylindrical object such as a riser (FIG. 5A).

Fairing 16 is secured to the riser 14 with bearing pads 32 that areconfigured to fit in the gap G in the shell 20 between the fins 22(FIGS. 5, 5A). Each bearing pad 32 has a curved inside surface 34, endportions 36 and side surfaces 38. The inside surface 34 has a curve thatcompletes the circle of the shell's circumference. The end portions 36are configured to fit in the space between the opposing edges 24, 26 andthe riser 14 and the side surfaces 38 are configured to align with thefins 22 (FIG. 5). In a preferred embodiment, the back portion 40 of theinside surface 34 is open (FIGS. 5, 5A, 7). The bearing pads 32 can besecured to the shell 20 by any number of means known to one skilled inthe art. An example of one securing means is a threadless bolt 42 (FIG.6A) with a washer and cotter pin 44 (FIG. 6B) in which the bolt isplaced through a pair of aligned openings 46 in fins 22 and in the sidesurfaces 38 of the bearing pad 32 (FIG. 5A).

The number of bearing pads 32 required to secure the fairing 16 to ariser 14 will depend upon the length of the fairing and the amount ofexternal forces being placed on the riser. For example, if a fairing hasa length of about 4½ feet, three bearing pads 32 spaced about 23 inchesapart, could be used to secure the fairing 16 to a section of the riser14 as illustrated in FIG. 5.

In an alternate embodiment, fairing 16A is formed from a cylindricalshell 20N having opposing fins 22N, extending outwardly in a verticaldirection, that define a longitudinal gap G (FIGS. 9 and 13). The spacedapart fins 22N are parallel to each other relative to the center of thecircle defining the shell and hence the circumference of the shell 20N(FIG. 13). The gap G in shell 20N provides an opening that allows forplacement of the shell 20N around a cylindrical object such as a riser.Fairing 16A also includes a flange 24 at its top 26 and bottom 28 edge,creating a top bearing surface 26N and a bottom bearing surface 28N forthe fairing 16A (FIGS. 9-13).

Flange 24 extends around the circumference of the shell 20N and extendoutwardly from the shell 20N about 3 to 4 inches. Optionally, flange 24includes at least one V-shaped cutout 70 to act as opening hinges forthe fairing 16A. In a preferred embodiment, the V-shaped cutout can bepositioned at the 12:00 o'clock, 3:00 o'clock and 9:00 o'clock positionof shell 20N in relation to the gap G at the 6:00 o'clock position.Alternatively, the V-shaped cutout can be placed anywhere on the flange24. The top and bottom edges 26F, 28F of fins 22N each include a tailsection 72 that extends outwardly from the flange 24 at the gap G. Theinside edge 74 of each tail section 72 is angled from the edge of thegap G to the outer edge 76 of each fin 22N. The angle depends on the finlength.

Fins 22N also include a first and second connector 78a, b that form aset of opposed connectors 78. Each fin 22N includes at least two sets ofconnectors, preferably three sets, for securing the fins 22N together inorder to attach them around a riser 14 (FIGS. 9-14). Each connector 78extends inwardly from the outside surface 80 of each fin 22N, creating acavity 82 that includes an opening 84 for receiving a fastening means.The walls of each connector 78 taper inward and the opening 84 is offsetfrom the center of the connector 78 toward the outer edge 76 of fin 22N.The cavity 82 of each connector 78a, b forms a rectangular shaped box 86that extends from the inside surface 88 of the fin 22N and is inhorizontal alignment with each tail section 72. In a preferredembodiment, a cover plate (not shown) can be secured over each of thecavity openings. Each connector 78a, b of the set is in parallelalignment with each other. The fastening means for securing the fins 22Ntogether can include male-female connectors 90, 92 or studs, nuts andwashers (not shown). In a preferred embodiment, the fastening means area male and female connector 90, 92 formed from 70 Shore D polyurethane,a 90-95 Shore A polyurethane or glass reinforced polyethylene (FIGS.15A, 15B). Alternatively, fiberglass/Inconel studs, nuts and washers canbe used. The male connector 90 is placed in one 78a of the set ofconnectors 78 and the female connector 92 is placed in the second 78b ofthe set of connectors 78 and the fasteners 90, 92 are secured together,drawing the fins 22N together, and thus the faring 16N, around raiser14. The connectors 78 include hand holes 94 for accessing the fasteningmeans (FIGS. 9, 11, 16, 17).

Shell 20, 20N has an outer diameter of D and fins 22, 22N have adistance between their ends of W. When W is equal to D the fins areparallel (FIG. 4). It has been found that if W decreases relative to D,i.e. the fins 22, 22N are tapered, the drag is reduced. In an alternateembodiment, fairing 16B is formed from a cylindrical shell 20P havingopposing fins 22P, extending outwardly in a vertical direction, thatdefine a longitudinal gap G. However, rather than being parallel, fins22P are tapered and thus, the distance of W is decreased between theopposing edges 23 of the fins 22P. (FIGS. 23-24) The placement of thefins 22P can be from W=D (parallel) to W=75% of D (tapered). Anydecrease of W in relation to D, will result in tapering of the fins 22P.A preferred ratio is W=25% of D which is about a 12.5% reduction foreach fin 22P, resulting in a 25% decrease in W with respect to D.

The fins are placed in a direction parallel with the fluid current inorder to move the boundary layer vortex eddies further away from theriser 14 without adding significant drag (FIG. 13). Fins 22N, 22P can beany length, however, regardless of the length, fins 22N, 22P do notextend beyond the nominal outer diameter of the shell 20. Preferably,fairing 16A, 16B has dimensions of length to diameter (shell diameter)such that the length to diameter ratio or aspect ratio is in the rangeof 1.50 to 2.50, preferably equal to or greater than 1.75 to 2.0.

Fairings 16, 16A, 16B would typically range in height from about 2 to 12feet and would typically have a diameter of about 6 to 48 inches. Theshell 20, 20N, 20P is rotatably mounted about a substantiallycylindrical element, such as the riser 14, and rotates around the riser14 to match the fins 22, 22N, 22P with the direction of the current.

Shells 20, 20N and 20P are configured to fit around riser 14 such thatthey provide for pressure equalization; allow for fluid to reach thebearing face of the shell 20, 20N for lubricating the bearing face withfluid; and to allow for the flow of fluid to retard marine growth. Theconfiguration of the shell also assists in the directional rotation ofthe shell 20, 20N, 20P around the riser 14 in order to align the fairing16, 16N, 16P with the current.

As shown in FIGS. 16 and 17, a fairing system is contemplated in which anumber of fairing segments 16, 16A, 16B can be installed on the riser 14to rotate independently along a longer elongated element. With fairingsegments 16A and 16B, the top and bottom bearing surfaces 26N, 28N ofthe flanges 24 allow each fairing segment 16A, 16B to freely rotate onthe adjoining flanges 24 (FIG. 16). In an alternate embodiment, eachfairing segment 16, 16A, 16B may be separated by a two-section collar 48configured such that it allows each fairing 16, 16A, 16B segment tofreely rotate on the collar 48 (FIG. 17). In one embodiment, thecircular collar 48 has an outside surface 50, a top surface 52, aninside surface 54 and end sections 56a, b (FIGS. 18, 19). The collar 48can be any height, for example in one embodiment it can be about 3inches. The diameter of the collar 48 will depend upon the diameter ofthe riser 14 it will encircle. The collar 48 also includes a pluralityof annulus spacers 62 placed around the inside surface 54 of the collar48. The annulus spacers 62 secure the collar 48 to the riser 14 andreduce rotational and axial movement of the collar 48 by inducing hoopstress and providing a frictional surface on the riser 14. The spacers62 extend outwardly from the inside surface 54 such that the ID ofannulus spacers 62 is smaller than the ID of the collar 48. The numberof spacers 62 on each collar will depend upon the circumference of thecollar. In one embodiment, at least six spacers 62 would be used.

Each annulus spacer 62 has a spacer face 64, and intermediate portion 66and a spacer retainer 68 (FIG. 20), The spacer retainer 68 is insertedthrough a spacer hole (not shown) in the inside surface 54 of the collar48. The spacer retainer 68 is sufficiently flexible that it may beelastically deformed to pass through the spacer hole in the insidesurface of the collar 48, while the spacer face 64 is sized to preventpassage through the spacer hole when a determined force is assertedagainst the spacer face 64. Annulus spacers 62 are constructed ofmaterial suitable to induce frictional interaction between the collar 48and the riser 14. For example, the spacers 62 can be formed from apolyurethane material that provides compliance so that when the twosections 48a, 48b of the collar are secured around the riser 14 there isradial compression from the inside surface 54 of the collar 48 onto theriser 14, thus compressing the polyurethane and causing friction. Thetwo sections 48a, 48b of the collar are placed around the riser 14 andsecured on the collar's underside 58 with a securing means such as abolt, nut and washer threaded through an opening in each of the endsections 56a, b. In a preferred embodiment, the collar will include aplurality of pressure relief holes 60 (FIGS. 14-15).

Fairings 16, 16A, 16B and collar 48 can be constructed from anynon-metallic, low corrosive material such as high or low densitypolyethylene, polyurethane, vinyl ester resin, poly vinyl chloride(PVC), or other materials with substantially similar flexibility anddurability properties or multilayer fiberglass mat. These materialsprovide fairings 16, 16A, 16B and collar 48 with the strength to stay onthe riser 14, but enough flex to allow it to be placed around the riser14 during installation. The use of such materials eliminates thepossibility of corrosion, which can cause the fairing shell to seize uparound the elongated element it surrounds.

FIGS. 21 and 22 present test results demonstrating the surprisingeffectiveness of the inventive fairing 16. FIG. 21 is a graph of dragcoefficient (Cd) for a bare pipe and the ADFS by Reynolds number (Re)and FIG. 22 is a graph of A* by nominal reduced velocity (Vm), which isdefined as Vm=U/(fn*D) where U is the tow velocity, D the cylinderdiameter and fn is the natural frequency of the system. A* is thenormalized vibration amplitude which is defined as A*=A/D. Forreference, the normalized vibration amplitude of a bare pipe would beexpected to be in the range of 0.9 to 1.0 so this fairing decreases theamplitude of vibration by significantly more than 90%.

These tests were conducted in a tow tank with the marine element towedto develop relative motion between the test sample and the water. Thetest sample was allowed to freely vibrate in the transverse direction.FIG. 21 illustrates the drag coefficient (Cd) for both a bare cylinderand a cylinder protected by the fairing 16. FIG. 22 illustrates thevelocity of both a bare cylinder and a cylinder protected by the fairing16. In both cases, the test sample was allowed to freely vibrate in thetransverse direction. Also shown are published curves of Cd by Reynoldsnumber for a fixed bare pipe. The transverse vibration setoff by VIVcauses a several-fold increase in Cd. With the fairing 16 installed,drag coefficients are significantly reduced relative to either fixed orfreely oscillating pipe to 0.4 or less. Further, the installation of thefairing 16 causes vibration to be reduced by at least 90% and by as muchas 95 to 99%. FIG. 22 also illustrates the surprising superior VIVsuppression performance of the inventive fairing 16, 16A, showing thatthe efficiency of the fairing 16, 16A is approximately 95%. A* for abare pipe is upwards of 0.8 while a pipe equipped with the inventivefairing possesses an A* of approximately 0.01. The graph illustratesthat the lateral vibrations caused by VIV are almost totally eliminated.

Tests results have shown, as illustrated in FIG. 25, that as W decreaseswith respect to D, the drag coefficient is reduced. The graph of FIG. 25shows Drag Coefficient (Cd) compared to Wind Velocity “V”, where eachline on the graph represents a different W:D ratio. Lines A1, A2represents a parallel fin arrangement where W=D; line B represents thedrag for a tapered fin where W=75% of D (W=0.75 of D); line C representsthe drag for a tapered fin where W=50% of D (W=0.50 of D); and line Drepresents the drag for a tapered fin where W=5% of D (W=0.05 of D)(nearly touching). Initially as distance of W is decreased from D thereis a large change in Cd. As the distance of W is decreased even furtherthe amount of reduction in Cd is less then when initially started. Ascan be seen from the graph in FIG. 25, a reduction in 25% of thedistance of W in relation to D at the beginning shows a large drop is Cd(difference between lines A1, A2 and line B), while the reduction of 50%of the distance W in relation to D to the reduction of 75% of thedistance of W in relation to D shows less of a change in Cd (differencebetween lines C and D). This trend continues till the point where thedistance of W is reduced to 0 and the fins 22P are touching.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A fairing for the reduction of vortex-inducedvibration, the minimization of drag and the elimination of the gallopingphenomenon about a substantially cylindrical element immersed in a fluidmedium, comprising: a one-piece fairing having a U-shaped cylindricalshell portion at comprising a leading edge of the faring with, opposingedges extending toward, and a trailing edge of the fairing, the opposingedges extending from the leading edge toward the trailing edge of theshell portion, the opposing edges further defining a longitudinal gaptherebetween that extends from the leading edge to the trailing edge ofthe shell portion, wherein the longitudinal gap provides an opening thatallows for placement of the substantially cylindrical element throughthe longitudinal gap and into the shell portion of the fairing; andparallellongitudinal fins extending outwardly from the opposing edges ofthe shell portion in which the parallellongitudinal fins taper inwardtoward the trailing edge of the fairing, wherein theparallellongitudinal fins are positioned so as to reduce vortex-inducedvibration and minimize drag on the cylindrical element.
 2. The fairingof claim 1, further including a bearing pad connector configured to fitin the gap in the shell portion between the shell's shell portion'sopposing edges and the parallel longitudinal fins.
 3. The fairing ofclaim 2, wherein the bearing pad has a curved inside surface and sidesurfaces in parallel alignment with each of the fins.
 4. The fairing ofclaim 2, wherein each fairing includes at least one bearing padconnector for securing the fairing to a cylindrical element, whereineach connector has a curved inside surface and side surfaces inalignment with each of the fins.
 5. The fairing of claim 4, wherein eachfairing includes a plurality of bearing pads connectors for securing thefairing to a cylindrical element.
 6. The fairing of claim 1, furtherincluding at least a set of opposed connectors for securing the fairingto a cylindrical element, each connector being positioned on an insidesurface of each parallel longitudinal fin.
 7. The fairing of claim 6,wherein the fins include a plurality of opposed connectors.
 8. Thefairing of claim 6, wherein each connector includes an openingconfigured to receive a fastening means for securing the opposingconnectors together.
 9. The fairing of claim 6, further including aflange at a top and bottom edge of the fairing, the flange extendingaround the circumference of the shell and outwardly from the shell. 10.The fairing of claim 9, wherein the flange includes at least oneV-shaped cutouts.
 11. The fairing of claim 1, wherein each fin does notextend beyond the outer diameter of the shell.
 12. The fairing of claim1, wherein the fairing is constructed from a non-metallic, low corrosivematerial selected from a group consisting of polyethylene, polyurethane,vinyl ester resin, poly vinyl chloride and fiberglass.
 13. The fairingof claim 1, wherein the shell portion has an outer diameter D and thelongitudinal fins have a distance W located between opposing edges endsof the longitudinal fins at the trailing edge of the fairing.
 14. Thefairing of claim 13, wherein the a ratio of W to D is from W=D W<100% ofD to W =75% of D.
 15. A fairing system for the reduction ofvortex-induced vibration, the minimization of drag and the eliminationof the galloping phenomenon about a substantially cylindrical elementimmersed in a fluid medium, the fairing system comprising: a pluralityof one-piece fairings having U-shaped cylindrical shell portions at,each shell portion comprising a leading edge of each shell portion, eachshell portion having, opposing edges extending toward, and a trailingedge of the fairing, the opposing edges extending from the leading edgetoward the trailing edge of the shell portion, the opposing edgesfurther defining a longitudinal gap therebetween that extends from theleading edge to the trailing edge of the shell portion, wherein thelongitudinal gap provides an opening that allows for placement of thesubstantially cylindrical element through the longitudinal gap and intothe shell portion; parallellongitudinal fins extending outwardly fromthe opposing edges of each of the plurality of shell portions in whichthe parallellongitudinal fins taper inward toward the trailing edge ofthe fairing, wherein the parallellongitudinal fins are positioned so asto reduce vortex-induced vibration and minimize drag on the cylindricalelement; and means for securing each of the plurality of fairings aroundthe cylindrical element.
 16. The fairing system of claim 15, wherein themeans for securing the fairings around the cylindrical element includesa bearing pad connector configured to fit in the gap in each shellportion between the shell's shell portion's opposing edges and theparallel longitudinal fins.
 17. The fairing system of claim 16, whereinthe bearing pad has a curved inside surface and side surfaces inparallel alignment with each of the fins.
 18. The fairing system ofclaim 16, wherein each fairing includes at least one bearing padconnector for securing the fairing to a cylindrical element, whereineach connector has a curved inside surface and side surfaces inalignment with each of the fins.
 19. The fairing of claim 15, whereinthe means for securing include at least a set of opposed connectors,each connector being positioned on an inside surface of each parallellongitudinal fin.
 20. The fairing of claim 19, wherein the fins includea plurality of opposed connectors.
 21. The fairing of claim 19, whereineach connector includes an opening configured to receive a fasteningmeans for securing the opposing connectors together.
 22. The fairing ofclaim 15, further including a flange at a top and bottom edge of thefairing, the flange extending around the circumference of the shell andoutwardly from the shell.
 23. The fairing of claim 22, wherein theflange includes at least one V-shaped cutout.
 24. The fairing system ofclaim 22, wherein the flanges on each fairing are configured such thatthey allows each fairing to freely rotate on an adjoining fairing. 25.The fairing system of claim 15, wherein a circular collar is positionedbetween each of the plurality of fairings, the collar configured suchthat it allows each fairing to freely rotate on the collar.
 26. Thefairing system of claim 25, wherein the collar is in two sections heldtogether by securing means for securing the collar around thecylindrical element.
 27. The fairing system of claim 25, wherein thecollar includes a plurality of compliant annulus spacers extendingoutwardly from an inside surface of the collar, the spacers beingconfigured to induce frictional interaction between the collar and thecylindrical element.
 28. The fairing system of claim 15, wherein eachfin does not extend beyond the outer diameter of the shell.
 29. Thefairing system of claim 15, wherein the fairing is constructed from anon-metallic, low corrosive material selected from a group consisting ofpolyethylene, polyurethane, vinyl ester resin, poly vinyl chloride andfiberglass.
 30. The fairing system of claim 15, wherein the shellportion has an outer diameter D and the parallel longitudinal fins havea distance W located between opposing edges ends of the fins at thetrailing edge of the fairing.
 31. The fairing of claim 30, wherein the aratio of W to D is from W=D W<100% of D to W=75% of D.
 32. The fairingof claim 13, wherein the ration ratio of W to D is from W=D W<100% of Dto W=50% of D.
 33. The fairing system of claim 30, wherein the rationratio of W to D is from W=D W<100% of D to W=50% of D.
 34. A fairing forthe reduction of vortex-induced vibration, the minimization of drag andthe elimination of the galloping phenomenon about a substantiallycylindrical element immersed in a fluid medium, comprising: a one-piecefairing having a U-shaped cylindrical shell portion at comprising aleading edge of the faring with, opposing edges extending toward, and atrailing edge of the fairing, the opposing edges extending from theleading edge toward the trailing edge of the shell portion, the opposingedges further defining a longitudinal gap therebetween that extends fromthe leading edge to the trailing edge of the shell portion, wherein thelongitudinal gap provides an opening that allows for placement of thesubstantially cylindrical element through the longitudinal gap and intothe shell portion of the fairing; parallellongitudinal fins extendingoutwardly from the opposing edges of the shell portion in which theparallellongitudinal fins taper inward toward the trailing edge of thefairing, wherein the parallellongitudinal fins are positioned so as toreduce vortex-induced vibration and minimize drag on the cylindricalelement; a flange at a top and bottom edge of the fairing, the flangeextending around the circumference of the shell portion and outwardlyfrom the shell portion; and at least a set of opposed connectors forsecuring the fairing to the cylindrical element, each connector beingpositioned on an inside surface of each parallel longitudinal fin.